Work-related asthma in Montreal, Quebec: population attributable risk in a community-based study.

BACKGROUND: Occupational exposures are an important cause of adult-onset asthma but the population attributable risk percentage (PAR%) has been less frequently studied. OBJECTIVES: To examine the distribution and determinants of adult asthma in six centres across Canada using data gathered in a community-based study. METHODS: Data were gathered in a community survey of 2959 adults using the European Community Respiratory Health Survey Protocol. A subsample of 498 subjects completed detailed health and occupational questionnaires, methacholine challenge tests and allergy skin tests. Asthma was defined in three ways: current wheeze, asthma symptoms and/or medication, and airway hyperresponsiveness. Occupational exposures were classified as sensitizers or irritants. Associations between asthma and occupational exposures were examined using logistic regression analysis. Model selection was based on the findings for current wheeze, and the same model was applied to the other definitions of asthma. RESULTS: Fifty-six per cent of subjects reported ever having had occupational exposure to sensitizers, and 9.8% to irritants. Current wheeze was associated with exposure to irritants (PAR% 4.54%), and airway hyperresponsiveness was associated with exposure to sensitizers (PAR% 30.7%). Neither a history of childhood asthma, atopy, nor confining the analysis to adult-onset asthma affected these associations. Analysis of effect modification suggested two types of work-related asthma: one due to exposure to occupational sensitizers, and the other due to exposure to irritants. CONCLUSIONS: Detailed assessment of past and current exposures is essential in the investigation of work-related asthma. Childhood asthma reactivated or aggravated by work exposures is not easy to distinguish from asthma induced by work, a misclassification that could lead to an underestimation of work-induced asthma. This should be taken into account in jurisdictions in which persons with work-aggravated asthma are not eligible for workers' compensation.

Airflow obstruction in young adults in Canada.

OBJECTIVE: Airflow obstruction is relatively uncommon in young adults, and may indicate potential for the development of progressive disease. The objective of the present study was to enumerate and characterize airflow obstruction in a random sample of Canadians aged 20 to 44 years. SETTING: The sample (n=2962) was drawn from six Canadian sites. DESIGN: A prevalence study using the European Community Respiratory Health Survey protocol was conducted. Airflow obstruction was assessed by spirometry. Bronchial responsiveness, skin reactivity to allergens and total serum immunoglobulin E were also measured. Logistic regression was used for analysis. RESULTS: Airflow obstruction was observed in 6.4% of the sample, not associated with sex or age. The risk of airflow obstruction increased in patients who had smoked and in patients who had lung trouble during childhood. Adjusted for smoking, the risk of airflow obstruction was elevated for subjects with past and current asthma, skin reactivity to allergens, elevated levels of total immunoglobulin E and bronchial hyper-responsiveness. Of the subjects with airflow obstruction, 21% were smokers with a history of asthma, 50% were smokers without asthma, 12% were nonsmokers with asthma and 17% were nonsmokers with no history of asthma. Bronchial hyper-responsiveness increased the prevalence of airflow obstruction in each of these groups. CONCLUSION: Smoking and asthma, jointly and individually, are major determinants of obstructive disorders in young adults. Bronchial hyper-responsiveness contributes to obstruction in both groups.

Childhood predictors of smoking in adolescence: a follow-up study of Montreal schoolchildren.

BACKGROUND: The factors that cause children to become smokers in adolescence remain unclear. Although parental smoking and peer pressure may play a role, physiological factors such as lung volume have also been identified. METHODS: To investigate these and other possible childhood predictors of teenage smoking, we gathered follow-up data on 191 Montréal schoolchildren, aged 5-12 years (average 9.2 yr) when first examined. At an average age of 13.0 years, they answered further questions on their health and smoking behaviour and provided a second set of spirometric measurements. RESULTS: At the second survey, 80% of the children had entered high school and 44% had become smokers. Reaching puberty between the surveys was the most significant determinant of becoming a smoker: 56.4% of the 124 children postpubertal at the second survey had taken up smoking, versus 17.9% of the 67 who were still prepubertal (p = 0.001). We found salivary cotinine level, a measure of uptake of environmental tobacco smoke, to be an independent predictor of becoming a teenage smoker; even after adjustment for sex, socioeconomic status of parents, a crowding index, and the numbers at home of siblings, adult smokers and cigarettes smoked, it remained significant for both groups: postpubertal (odds ratio [OR] 1.2, 95% confidence interval [CI] 1.2-3.0) and prepubertal (OR 2.1, 95% CI 1.0- 4.5). The influence of forced vital capacity was marginally significant only in the postpubertal group (OR 5.0, 95% CI 0.88-28.3). INTERPRETATION: The proportion of nicotine absorbed from that available in environmental tobacco smoke during childhood is associated with subsequent smoking in adolescence. The more efficient absorption of nicotine seen in some children may be related to physiological factors such as lung capacity.

Geographic and gender variability in the prevalence of bronchial responsiveness in Canada.

OBJECTIVES: Geographic variability in reported prevalences of asthma worldwide could in part relate to interpretation of symptoms and diagnostic biases. Bronchial responsiveness measurements provide objective evidence of a common physiologic characteristic of asthma. We measured bronchial responsiveness using the standardized protocol of the European Community Respiratory Health Survey (ECRHS) in six sites in Canada, and compared prevalences across Canada with international sites. DESIGN: Samples of 3,000 to 4,000 adults aged 20 to 44 years were randomly selected in Vancouver, Winnipeg, Hamilton, Montreal, Halifax, and Prince Edward Island, and a mail questionnaire was completed by 18,616 individuals (86.5%). Preselected random subsamples (n = 2,962) attended a research laboratory for examination including more detailed questionnaires, lung function testing including methacholine challenge, and skin testing with 14 allergens. RESULTS: Prevalences of bronchial hyperresponsiveness, measured as cumulative dose of methacholine required to produce a 20% fall from the post-saline solution FEV1 < or = 1 mg, ranged from 4.9% (95% confidence interval [CI], 1.6 to 8.5) in Halifax to 22.0% (95% CI, 18.1 to 26.0) in Hamilton (median, 10.7%). In all Canadian sites, bronchial hyperresponsiveness was more prevalent in women than in men. Neither the geographic nor gender differences were accounted for by differences in age, smoking, skin test reactivity, or baseline FEV1. Geographic- and gender-related variability changed little when only bronchial hyperresponsiveness associated with asthma-like symptoms was considered. CONCLUSIONS: A wide variability in bronchial responsiveness can occur within one country, almost as wide as the range found across all international sites participating in the ECRHS study and not explained by differences in gender, smoking, skin test reactivity, and FEV1. While gender variability in the prevalence of bronchial responsiveness is likely due to hormonal and immunologic factors, geographic variability is likely to result from environmental factors.